imageencoding

Image encoding is the process of converting image data into a coded representation suitable for storage or transmission. It typically involves compression to reduce size and may be lossy or lossless. The choice of encoding affects image quality, file size, and compatibility across devices and software.

Lossless encodings reproduce the original image exactly. PNG uses deflate compression and supports transparency; TIFF can employ several lossless schemes; GIF is lossless for indexed color but limited to 256 colors and is often used for simple animations.

Lossy encodings discard information to achieve higher compression. JPEG is the dominant format for photographs, using transform coding, quantization, and entropy coding with optional chroma subsampling. Modern formats such as WebP, HEIC/HEIF, and AVIF use advanced codecs (VP9, HEVC, or AV1) and provide improved compression at similar quality, with support for transparency and animation in many cases.

Image formats differ in features, such as color depth, transparency, metadata, and browser or software support. On the web, JPEG, PNG, and WebP are common; for animations, GIF or APNG; for archival storage, TIFF or RAW variants. Decoding is the reverse process and must be supported by software to render the image.

Technical considerations include color space (often sRGB), bit depth (8-bit or higher), and metadata (EXIF, XMP). Encoding parameters trade off between quality and file size and may vary by format and use case.